The field engineer was not able to determine the cause or find a way to fix it. He doesn't know why it is happening but he doesn't think it should happen. He took lots of data from the computer and will send it to GM Engineering for analysis. It is interesting to note that the engineer determined that if this fan is turned on before starting the car then the a/c will not come on unless the a/c button is pressed. This is very interesting. It's not a solution but it's a work-around I can live with.